The chp package

The Communicating Haskell Processes (CHP) library is an
implementation of message-passing concurrency ideas from
Hoare's Communicating Sequential Processes. More details and
a tutorial can be found at its homepage:
http://www.cs.kent.ac.uk/projects/ofa/chp/, and there is
also now a blog with examples of using the library:
http://chplib.wordpress.com/. The library requires at
least GHC 6.8.1.